1. Field of the Invention
The present invention relates generally to a copper/indium/gallium/selenium (CIGS) solar cell and a method for fabricating the same, and more particularly, to a CIGS solar cell including a thermal expansion buffer layer configured between an alloy thin film layer and a CIGS thin film layer, and a method for fabricating the same.
2. The Prior Arts
CIGS thin film solar cells are being expected as one type of the most potentially low cost solar cells. Comparing with the other current thin film battery technologies, a CIGS thin film solar cell has higher efficiency. Currently, a small size CIGS thin film solar cell unit may achieve an efficiency of up to 19%, and a large size one may achieve an efficiency of up to 13%. Further, the CIGS thin film solar cell can be fabricated by a chemical vapor deposition (CVD) process which is adapted for low cost and large size processing. Furthermore, the CIGS thin film solar cell is radiation resistible and light weighted.
FIG. 1 is a schematic diagram illustrating a conventional CIGS thin film solar cell 1. Referring to FIG. 1, the CIGS thin film solar cell 1 includes a substrate 10, a molybdenum thin film layer 20, an alloy thin film layer 50 and a CIGS thin film layer 80. The molybdenum thin film layer 20 is deposited by sputtering on the substrate 10 for serving as a back electrode. The alloy thin film layer 50 is deposited by sputtering on the molybdenum thin film layer 20 for improving the electrical conductivity and reducing the resistance coefficient. The CIGS thin film layer 80 is then configured on the alloy thin film layer 50 by a synchronizing evaporation deposition or a selenylation process for serving as a light absorbing layer of the CIGS solar cell 1.
However, when such a CIGS solar cell 1 is exposed under the sunlight which causes the temperature raises, the difference of thermal expansion coefficient between the alloy thin film layer 50 and the CIGS thin film layer 80 may cause the films cracking or peeling off. This may impair the photoelectric transformation efficiency of the CIGS solar cell 1, or even destroy the CIGS solar cell.
As such a CIGS solar cell resistive to the stress caused by the thermal expansion difference is desired for solving the problem existed in the conventional technology.